astronomy Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall evolution. Objects of interest includ ...

, a glitch is a sudden small increase of around 1 part in 1 million in the rotational

frequency Frequency is the number of occurrences of a repeating event per unit of time. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio ...

of a

pulsar A pulsar (''pulsating star, on the model of quasar'') is a highly magnetized rotating neutron star that emits beams of electromagnetic radiation out of its Poles of astronomical bodies#Magnetic poles, magnetic poles. This radiation can be obse ...

, which usually decreases steadily due to braking provided by the emission of radiation and high-energy particles. It is not known whether glitches are related to the

timing noise A pulsar (''pulsating star, on the model of quasar'') is a highly magnetized rotating neutron star that emits beams of electromagnetic radiation out of its magnetic poles. This radiation can be observed only when a beam of emission is pointin ...

which all pulsars exhibit. Following a glitch is a period of gradual recovery where the observed periodicity slows to a period close to that observed before the glitch. These gradual recovery periods have been observed to last from days to years. only multiple glitches of the

Crab Crabs are decapod crustaceans of the infraorder Brachyura (meaning "short tailed" in Greek language, Greek), which typically have a very short projecting tail-like abdomen#Arthropoda, abdomen, usually hidden entirely under the Thorax (arthropo ...

and Vela pulsars have been observed and studied extensively.

Cause

While the exact cause of glitches is unknown, they are thought to be caused by an internal process within the pulsar. This differs from the steady decrease in the pulsar's rotational frequency, which is caused by external processes. Although the details of the glitch process are unknown, it is thought that the resulting increase in the pulsar's rotational frequency is caused by a brief coupling of the pulsar's faster-spinning

superfluid Superfluidity is the characteristic property of a fluid with zero viscosity which therefore flows without any loss of kinetic energy. When stirred, a superfluid forms vortex, vortices that continue to rotate indefinitely. Superfluidity occurs ...

core to the crust, to which it is usually not coupled. This brief coupling transfers angular momentum from core to surface, which causes a decrease in the measured period.

Implications

If the mechanism is as suggested above, observed pulsar glitches set a limit on the

moment of inertia The moment of inertia, otherwise known as the mass moment of inertia, angular/rotational mass, second moment of mass, or most accurately, rotational inertia, of a rigid body is defined relatively to a rotational axis. It is the ratio between ...

of the pulsar being observed and, thus, the mass-radius relation possible in dense nuclear matter. More generally, observations of pulsar glitches allow indirect information on the dense nuclear matter in neutron star interiors to be inferred, in particular its superfluid properties.

References

* * https://web.archive.org/web/20051018233130/http://www.saao.ac.za/~wgssa/as4/urama.html http://www.saao.ac.za/~wgssa/as4/urama.html * {{Neutron star Rotation-powered pulsars

Cause

Implications

See also

References